Various material tests must be performed during the search for new materials for contact lenses. As the properties of the lens change under moisture, the sample for the test is placed in a salt water solution. The task is to measure the geometric changes of the lenses when they are expanded and heated in hydration chambers. This object cannot be measured using conventional measurement technology as the lens is hardly visible in the liquid. Therefore, the high quality optoCONTROL 2600 which measures the geometry of the lens using the slight weakening of the emitted light beam is used for this task. The unique, dynamic threshold function enables a fine adjustment of the sensor and thus the optimum recognition of the edges of the sample.